The stability conjecture for infinite set-homogeneous hypergraphs

Let k3k\geq 3, and let HH be an infinite set-homogeneous kk-hypergraph whose theory is stable, meaning that it does not have the order property: there are no formula ϕ(xˉ,yˉ)\phi(\bar{x},\bar{y}), model MM, and sequences (aˉi)iω(\bar{a}_i)_{i\in\omega} and (bˉj)jω(\bar{b}_j)_{j\in\omega} such that Mϕ(aˉi,bˉj)M\models\phi(\bar{a}_i,\bar{b}_j) if and only if i<ji<j. A kk-hypergraph is complete if every kk-element subset is a hyperedge, and its complete complement is obtained by replacing the hyperedge relation with its complement.

The stability conjecture. Any infinite set-homogeneous kk-hypergraph with stable theory is complete or has complete complement.

This predicts that stability forces an infinite set-homogeneous kk-hypergraph to be trivial up to complementation. The supplied text poses the statement without indicating whether it is known or resolved.

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Primary source

Amir Assari, Narges Hosseinzadeh and Dugald Macpherson, “Set-homogeneous hypergraphs”, arXiv:2202.09613 (2022).

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